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Heart Pressures
Atrial systole
- During atrial systole, pressure in the two atria exceeds the resistance of the ventricles.
- This forces the tricuspid and mitral valve to open
- Atrial ejection occurs
- atrial kick 20-30% of cardiac output
- Blood flows from higher to lower pressure
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Ventricular systole:
- During ventricular systole, pressure in the two ventricles exceeds the resistance of the outflow vessles.
- Tricuspid and mital valves close
- Pulmotic and aortic valves open
- Ventricular ejection occurs
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What is Preload?
- The volume of blood filling the ventricles at the end of diastole(just before systole occurs)
- RV=CVP(central venous pressure)
- LV=Pulmonary artery end diastolic pressure
- PCWP (Capillary wedge pressure
- These are all filling pressures
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Assessment of right heart preload
- Increased R heart preload =
- -JVD
- Ascities
- Hepatic engorgement
- peripheral edema
- Decreased R heart pressure
- Poor skin tugor
- Dry mucus membranes
- Orthostatic hypotension
- Flat jugular veins
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Assessment of Left sided preload
- Increased L heart pressure
- Dyspnea
- cough
- third and fourth heart sound
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Starlings Law
- The force of a contraction of cardiac muscle is dependent on the stretch of cardiac muscle fibers
- Larger the stretch....larger the contraction=good co
- Preload is the mechanism that stretches ventricular fibers
- The force of ventricular contraction is dependent on preload
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Factors affecting preload
- Blood volume
- -hypovolemia (dehydration)
- -hypervolemia (fluid overload)
- Atrial contracion
- -Atrial kick 25-35%
- -loss of atrial kick d/t afib
- Venous return to heart=how much blood returns to the heart
- -Physical factors=stenosis
- -medication factors
- Cardiac muscle fibers
- -Heart failure
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What is Afterload?
- Resistance to ejection of blood from ventricles
- The pressure the ventricle must generate to overcome resistance to ejection(systole)
- The amount of energy the LV has to generate to push the blood through the body
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Afterload
- Increasing afterload increase the workload of the heart therefore increasing the O2 demand of the heart.
- Afterload measured by systemic vascular resistance (SVR)
- dialted blood vessels = decreased SVR
- Constricted blood vessels = increase SVR
- Normal SVR is 800-1200
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What is contractility?
- Ability of the cardiac muscles fibers to shorten in length
- Increased muscle fibers shortning = increased contractility= increased squeezed
- Inotrophy agents can affect contractility
- positive increases-ex: digoxin
- negative decreases ex: beta blockers, calcium channel blockers
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Diagnostic testing: Labs
- Creatine Phosphokinase CPK onset 4-12 hrs post damage
- Troponin- found in cardiac muscle - onset 3-4 hrs post damage
- B-type natriuretic peptide (BNP)
- Hormone released from ventricles when there is an increase in preload. Normal is 100
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The Pulmonary artery catheter (Swan Ganz)
- Most invasive of critical care monitoring
- Known as the swan-ganz or right heart catheter
- Simutaneously assesses seveal hemodynamic parameters
- Pumonary artery systole and diastolic pressures
- pulmonary artery occulsion
- cardiac output
- central venous pressure
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Swan
- RA=right atrium =cvp 2-6
- RV=right ventricle systolic= squeeze 20-30
- and diastolic = relaxed 2-8
- PA=pulmonary artery
- systole 20-30
- diastolic 8-15
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CVP
- Measures filing pressures of the right heart
- Measures the fluid status
- Normal CVP (RA) =2-6
- Low cvp = hypovolemia, dehydration and when bleeding occurs, vasodilation and diuresis
- High CVP= fluid overload, occurs in CHF and accure MI, also in renal failure
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PA pressures
- Measures systole and diastole pressures of the pulmonary artery
- reflects the state of RV and lung
- systole = 20-30 and diastole = 8-15
- Low pa = hypovolemia
- High pa = Fluid overload/CHF
- mitral stenosis
- lung disease COPD
- Pulmonary embolis
- Idopathic pulmonary heypertension
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Pulmonary artery Wedge Pressure
- Wedge pressure reflects blood pressure in the LV at the end of diastole
- Wedge measures of the Left vetricular preload (left filling Pressure)
- Low wedge = hypovolemia
- High wedge=fluid overload, MI, cardiogenic shock, CHF
- Normal wedge = 4-12 for the entire left side
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What is cardiac output?
- The amount of blood ejected by the heart per minute
- Normal CO=4-8 l/min
- CO =HRxSV
- stroke volume is the amount of blood ejected by the heart SV= 50-100ml
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Cardiac Index
- Cardiac Index is cardiac output divided by body surface area
- CI =CO/BSA
- BSA is determined by ht and wt
- Normal is 2.4-4 l/min
- CI less that 2 = shock state
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Septic shock
- Characterized by bacterial endotoxins
- endotoxins produce massive arterial vasodialation
- severe decrease bp
- decreased SVR less than 600 (normal 800-1200)
- The heart compensates by increasing the HR and contractility=increased CO
- heart beats faster and harder
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Cardiogenic Shock
- Characterized by nonfunctioning ventricular wall
- Heart loses pumping ability
- severe decrease in BP
- decreased CO
- vascular system compensates by vasoconstriction
- SVR increases above 1600
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Complications of the SWAN
- Pneumothorax
- infection
- balloon rupture
- pulmonary infarction
- pulmonary artery rupture
- ventricular tachycardia
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Review of Must Know numbers
- CVP-measures rt sided fluid status 2-6
- PA - pressure in the pulmonary artery systolic 20-30 and diastolic 8-15
- CO -blood flow through heart in liters 4-8
- CI- standardize measure of CO/BSA 2.4-4
- PCWP (wedge) Left ventricular preload 4-12
- SVR - systemic vascular resistance 800-1200
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